Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $57.88   3.614%   $59.9718   $59.97   $59.95   $60.00  
  Purchase #2 $6.36   7.542%   $6.8397   $6.84   $6.85   $6.80  
  Purchase #3 $195.30   13.226%   $221.1304   $221.13   $221.15   $221.10  
  Purchase #4 $97.81   9.694%   $107.2917   $107.29   $107.30   $107.30  
  Purchase #5 $86.36   6.857%   $92.2817   $92.28   $92.30   $92.30  
  Purchase #6 $45.99   8.157%   $49.7414   $49.74   $49.75   $49.70  
  Purchase #7 $106.94   8.258%   $115.7711   $115.77   $115.75   $115.80  
  7 purchase totals = $596.64       $653.0278   $653.02   $653.05   $653.00